Conventionally, a coke-oven plant comprises a large number of coke ovens in the form of a battery. Along one side of the battery (commonly referred to as the machinery, or pusher side) coke-levelling and pressing equipment (to level coke in the coke ovens after loading, and to press coke from the ovens on completion of coking) travels. Along the other side of the battery (commonly referred to as the coke side) a coke truck (which collects coke as it is pressed from a coke oven and conveys it to a quenching station) travels.
In a system for handling coke-oven charge gases, the charge gases are withdrawn from the coke oven by extractor units which are mounted on a charge truck, such extractor units drawing off the charge gases from charge openings (while charging the coke oven) and delivering the gases to combustion and washing units. However, this method of withdrawing the charge gases has the disadvantage that fine particles of coal tend to be carried along with the gases. This results in rather significant ejecton of coal when a strong suction unit is used. Moreover, the combustion unit (arranged in succession with the extractor unit), while being designed to burn the charge gases, is not capable of satisfactorily handling coal particles. Consequently, operational faults are likely to occur if too many particles of coal are drawn into the system. Thus, where charge gas extractor units are associated with the charging truck, it is necessary to provide a separator burner in asociation with each suction port so that gas, which has been drawn from a corresponding charge opening, can be burnt.
In order to avoid the drawbacks associated with such conventional charge-gas extractor units, the charge gases are drawn through an updraft pipe of the coke oven, which is being charged, since updraft pipes are arranged in such a way as to minimize the likelihood of particles of coal being carried out of an associated oven chamber. The application of an intensive suction draft to the updraft pipe yields substantially better results than the formerly-conventional, less intensive evacuation by suction at an individual charge opening.
However, in the evacuation of charge gas through an updraft pipe, gas flow rates are necessarily very high and far in excess of the capacity of conventional combustion and washing units mounted on the charge truck. For this reason, where charge gases have been drawn off through updraft pipes, it is customary to introduce aspired gases into a main collector pipe (associated with the updraft pipes) and from which the gases flow to high capacity combustion and washing units. However, due to the unfavorable chemical composition of the charge gases, this has tended to cause undesirable incrustation and congestion in the collector pipe after a very short time.
The high flow rates of charge gas, drawn off through an updraft pipe during charging, have previously made it unfeasible to provide an extractor, combustion unit and washing system which is either adapted to be driven along the coke-oven ceiling or combined with the charging truck.
Commercial coke-oven chambers are normally 20-ton chambers, which typically produce in the range of from 200 to 400 and, in exceptional cases, up to 700 cubic meters per minute of charge gas. Smaller coke-oven chambers ordinarily yield charge gas at approximately the same or at a slightly lower rate, but the total volume is smaller. The ignition temperature of charge gas varies considerably with its composition, and the first fraction, i.e. that produced during the first, e.g., ten seconds, from any batch or charge often has poor ignition properties. Although ignition temperature, per se, is not generally measured, its effects are reflected in the temperature of the charge gas during its passage from the coke oven through a combustion chamber. Charge gas leaves a coke oven at a temperature in the approximate range of from 300.degree. to 600.degree. C; after ignition the corresponding range is from 1200.degree. to 1400.degree. C. Ignition requires a heat level; an electric spark, e.g., is inadequate for ignition.
As coke oven charge gas varies considerably in composition, the time required for complete burning at established temperatures varies likewise. The variation is, e.g., from about 0.3 to about 0.6 second; complete burning is assured over a period of one second at ignition temperature or above.
Each of, e.g., from 70 to 200 coke-oven chambers in a battery is recharged every 18 to 24 hours. There are from 4 to 8 charges made per hour depending on the number of chambers in a battery or plant. From each charge gas is produced for a period of from 3 to 5 minutes.
There are thus periods, which range in duration from 2.5 to 12 minutes, during which a combustion chamber is virtually free of any charge and during which it quickly cools to a temperature below that sufficient to ignite charge gases in the absence of supplementary heat, such as that provided by a separate burner.